Method of producing frames for grid electrodes



G. SAMUELS 3,226,803 METHOD OF PRODUCING FRAMES FOR GRID ELECTRODES Jan. 4, 1966 4 SheetsSheet 1 Filed Aug. 21, 1961 3 W T 0 Z W W A w Jan. 4, 1966 G. SAMUELS METHOD OF PRODUCING FRAMES FOR GRID ELECTRODE 4 Sheets-Sheet 5 INVENTOR. fi eA/w JAM/45 BY ATTOQ/VEV Filed Aug. 21

G. SAMUELS METHOD OF PRODUCING FRAMES FOR GRID ELECTRODES Filed Aug. 21, 1961 Jan. 4, 1966 4 Sheets-Sheet 4 INVENTOR. @FRARD J/wuas B Y spacings between the side rods.

United States Patent 3,226,803 METHSD 6F PRUDUCHNG FRAMES FGR Gltll) EL'E CTRUDES Gerard Samuels, Teaneclr, Nah, assiguor to Radio Corporation of America, a corporation of Delaware Filed Aug. 21, 1961, Ser. No. 132,651 3 (Claims. (Cl. 29-1555) This invention relates to a method of producing frame grid electrodes for electron discharge devices.

In certain types of electron tubes wherein it is desirable to employ grid electrodes having closely spaced and very fine lateral wire turns, it is often necessary to use grid electrodes known as frame grids. These grids comprise a frame including a pair of parallel side supports or side rods usually of circular cross section spaced apart by cross straps extending between and secured adjacent each end of the side rods. The lateral wire is wound about the frame and supported thereby.

According to one method of fabricating such grid frames, the side rods are fed into a welding machine in a direction at right angles to the cross straps. The cross straps are first Welded to one side rod, a mandrel is inserted between that side rod and a second side rod, and the cross straps are then welded to the second side rod. F or increasing the rate of production of frames according to this method, the cross straps when welded to the second side rod are simultaneously welded to another side rod of a second frame, the two side rods having been fed into the welding machine in closely adjacent relation. Thereafter the cross straps extending between the adjacent side rods are cut to separate the two frames. The mandrel is then inserted between the side rods of the sec ond frame to repeat the cycle.

One problem associated with the fabrication of frame grids by the method described is that it has been found difiicult to provide frames having closely controlled That is, although a mandrel is provided for controlling the spacing between the side rods of each frame, frames having non-parallel side rods are often produced due to the diiliculty of maintaining the side rods firmly against the mandrel during welding. One reason for this is that the side rods are not perfectly straight as they are fed into the welding machine and against the mandrel. The wires come from wire spools, and although first passed through a wire straightening device, some curl remains in the wires. Upon welding, the welding electrodes thus often engage the round side rods off center. This results in a rolling and displacement of the side rods from their desired position against the mandrel. A further reason why it is difficult to provide frames having parallel side rods using the apparatus described is that while a side rod positioning mandrel is provided for controlling the side rod spacing of the two side rods of the first frame, it has been difiicult when fabricating frame of small size (for reasons which will be disclosed hereinafter) to provide positive positioning means for the side rod of the second frame. Thus, upon welding, this latter side rod is relatively free to move from its desired position.

This problem is further aggravated by the fact that in a recently designed grid frame it is desirable that the cross straps extend beyond the side rods of each frame a predetermined length. Because of this it is necessary that the two adjacent side rods of adjacent grid frames be welded to the cross straps in spaced apart relation whereby the freedom of movement of the side rods is further increased. Hence, not only has it been found difiicult to maintain the parallel spacing of the side rods while fabricatin frames of this type, but it has also been found difficult to provide such grid frames having extending cross straps of desired length.

3,226,893 Patented Jan. 4 1966 A still further problem is the difiiculty encountered in the prior art method of maintaining the cross straps in proper relation with respect to the side rods during frame fabrication. In the prior art method described, guide combs are provided through which the cross straps are fed to the side rods. To avoid interference with the operation of the welding electrodes, however, these combs must be spaced at some distance from the side rods whereby close control of the relative positioning of the cross straps with respect to the side rods has not been easily obtainable. As known, frames having improperly positioned cross straps produce undesirable variations in the electrical characteristisc of electron tubes using the frames.

it is therefore an object of this invention to provide an improved method for fabricating grid frames of the types described.

Particularly, an object of this invention is to provide an improved method for fabricating grid frames of the types described wherein the spacing between the side rods, the length of the cross straps extending beyond the side rods, and the positioning of the cross straps with respect to the side rods are more accurate than in. the prior art.

For achieving these objects in accordance with this invention, a method is provided wherein the frame straps are fed transversely of a mandrel and sets of side rods, and wherein the cross straps are welded to adjacent side rods of two separate grid frames. For welding the cross straps to the side rods, a pair of oppositely disposed welding electrodes are provided, the electrodes being movable into engagement with the cross straps and side rods, and at least one of the welding electrodes serving also to accurately separate the side rods.

According to one embodiment of the methodof this invention, each of the welding electrodes is provided with at least one projection or tongue adjacent its end. Each tongue extends toward the other welding electrode and each has a generally decreasing cross section or wedge shape having its narrowed portion facing the other electrode. Upon movement of the welding electrodes into engagement with the grid frame elements, the tongues are inserted between the two adjacent side rods. The tongues wedge the two side rods apart, one of the side rods being pressed firmly against the mandrel and the other adjacent side rod being pressed firmly against a back-up plate. The side rods are thus maintained in proper parallel spaced apart relation during welding. Also, the side rods are spaced apart to provide the desired extending lengths of cross straps.

According .to another embodiment of the method of this invention, each welding electrode is provided with an extending portion or ridge along substantially the entire length of the electrode. The ridges are also wedge shaped and each ridge is provided with a transverse groove adjacent the ends thereof. During welding, the Welding electrodes are moved into engagement with the cross strap and side rods so as to insert the ridges between the adjacent side rods and to position the grooves astride the cross straps. By these means, as Will be described more fully hereinafter, the side rods are maintained in properly spaced apart relation and the cross straps are properly positioned with respect to the side rods.

FIG. 1 is a view in perspective of one type of grid frame which may be made by the method of this invention;

FIGS. 2 and 3 are fragmentary views in perspective illustrating the manner in which a lateral wire may be secured to the grid frame shown in FIG. 1;

FIG. 4 is a view in perspective showing parts of a grid frame fabricating apparatus invention;

FIG. 5 is a partial plan view of the apparatus shown in FIG. 4 but at a later step in the grid frame fabricating cycle;

FIG. 6 is a sectional view taken along line 6-6 of FIG.

FIG. 7 is a sectional viewtaken along line '77 of FIG. 5;

FIG. 8 is a view in perspective showing parts of another embodiment of a frame fabricating apparatus;

FIG. 9 is a view similar to FIG. 8 but at a later step in the grid frame fabricating cycle;

FIG. 10 is a view along line 1010 of FIG. 9, and;

FIG. 11 is a view similar to FIG. 10 but showing still another embodiment of a frame fabricating apparatus.

The grid electrode frame 10 shown in FIG. 1 comprises a pair of spaced apart parallel side rods 11 of circular cross section and two pairs of cross straps 12 extending between the side rods and secured adjacent each end thereof. The cross strap pairs 12 are secured to the side rods 11 as by welding, and each cross strap has a length, or ear 13, which extends beyond the side rods. The purpose of ears 13 is to secure the end of a lateral wire 15 to the grid frame as shown in FIGS. 2 and 3. To do this, the leading end of a lateral wire 15 may be first threaded between cars 13 and along a side rod 11 (FIG. 2) and the ears 13 then crimped against the side rod 11 (FIG. 3) to clamp the lateral wire therebetween.

In FIG. 4 is shown apparatus for fabricating grid frames of the type shown in FIG. 1, theapparatus including a pair of guide combs through which the cross straps 12 are fed. The cross straps 12 are provided from supply spools, not shown, and are fed in the direction of arrow A through guide combs 20 to the welding portion of the apparatus. Pairs of adjacently located side rods 22 and 23 are fed from supply spools, not shown, in the direction of arrow B so as to extend between and transversely to the pairs of cross straps 12. For welding the cross straps 12 to the side rods 22 and 23 and for providing the proper spacing between the side rods and the proper length of the ears 13, a pair of elongated opposing welding electrodes 25 and 26 are provided. The details of construction of the welding electrodes 25 and 26 and the manner in which the welding electrodes perform these functions will be described hereinafter. Although not shown, means for feeding side rods 22 and 23 may comprise known moveable chuck means adapted for grasping the side rods and advancing them in the desired direction. Also, means are provided for moving welding electrodes 25 and 26 transversely of their lengths and towards each other. Such means are not shown but may comprise cam and linkage arrangements known in the mechanical arts.

Oppositely disposed cutters 28 and 29 are provided for cutting the cross straps 12 extending between the adjacent side rods 24 and 48, and cutters 31 are provided for cutting the side rods 22 and 23. Also provided is a mandrel 32. Mandrel 32 has a slot 34 therein which divides the mandrel into two sections 36 and 38. Section 36 is of such size as to fit between side rods 23 and 24 of a grid frame 40 for providing proper spacing therebetween, and section 38 serves as a back-up plate for side rod 22. :Slot 34 is of such width as to receive the side rods 22 and 123 in proper spaced apart relation.

As mentioned, one problem of the prior art is the difficulty of preventing movement of the side rods during welding. It has been suggested that longitudinally extending grooves could be provided in place of the straight sides 42, 43 and 44 of the mandrel sections 36 and 38 shown in FIG. 6. Such grooves would reduce the amount of movement of the side rods by providing positive receiving and positioning means for the side rods. It has been found, however, that due to the small size of the grid frames and the corresponding small size of the mandrel 32, it is difficult to machine the mandrel to such desired cross sections. In one embodiment, for example, the frame side rods have a diameter of 31 mils and are spaced apart 100 mils. Mandrel section 36, which fits between the two side rods 23 and 24 of frame 40, as mentioned, has a width of mils and a thickness of but 35 mils. Mandrel section 33 has a somewhat larger cross section than section 36 as shown in FIGS. 4, 6 and 10, but the thickness of the narrow end 44 thereof which acts on side rod 22 is but 15 mils.

' The operation of the apparatus shown in FIG. 4 will now be described. As shown, the apparatus is at an intermediate step in the grid frame fabricating cycle, the cross strap pairs 12 having already been welded to the two side rods 4-8 and 49 of a frame 50 and also to one side rod 24 of frame 46, side rod 24 being adjacent to side rod 48. Mandrel 32 is then moved forward in the direction of arrow C so as to engage the side 42 thereof with side rod 24. Two side rods 22 and 23 are then fed in the direction of arrow B from the side rod supply spools and into slot 34 of mandrel 32 as shown in FIG. 5. The two side rods 22 and 23 are fed in closely adjacent relation to one another and lie in a plane extending through side rod 24 (PEG. 6) and the longitudinal axis of mandrel section 36. The welding electrodes 25 and 26 are then moved transversely of their length and towards one another so as to engage the cross strap pairs 12 and the side rods 22 and 23. As will be described hereinafter, the welding electrodes clamp the cross strap pairs against the side rods 22 and 23 and press and maintain the side rods 22 and 23 against the mandrel sections 36 and 38 in properly spaced, parallel relationship. The cross straps are then welded to the side rods. Cutters 28 and 29 are moved together to cut the cross strap pairs 12 between side rods 24 and 48 and to separate frame 50 from frame as (FIG. 6) and cutters 31 (FIG. 4) cut the side rods 22 and 23 to proper length. Mandrel 32 is then moved in the direction of arrow D conveying frame 46 along therewith and pulling additional lengths of cross straps 12 through guide combs 20 from the cross strap supply spools. Frame 45 is thus moved to the position just occupied by frame 53. Mandrel 32 is then retracted from within frame 459 and moved in the direction of arrows E and F to the position shown in FIG. 4. This completes the frame fabricating cycle.

As mentioned, the welding electrodes perform the functions of welding the cross straps to the side rods and providing the proper parallel spacing between the side rods. For accomplishing these purposes, each electrode may be provided with a projection which extends outwardly from the face thereof and towards the opposing electrode.

According to one embodiment of the apparatus as shown in FIGS. 5, 6 and 7, one welding electrode 25 may be provided with a projection or tongue 55 adjacent each end thereof. Each tongue has a generally decreasing, or tapering cross section, and has a length or height slightly less than the diameter of the frame side rods. Upon movement of the welding electrodes 25 and 26 towards one another (FIGS. 6 and 7), the tongues are inserted or wedged between the two adjacent side rods 22 and 23 and tend to force them apart. At full insertion, that is when the faces 56 and 57 of the welding electrodes 25 and 26 engage the cross straps 12, the side rods 22 and 23 are spaced apart the proper amount to provide the correct length of cross strap cars 13. Further, the side rods 22 and 23 are firmly pressed against mandrel sections 36 and 38, respectively. If desired, additional tongues may be provided intermediate the ends of the electrodes to provide further pressing action. Also, tongues may be provided on each electrode. Current is passed through the welding electrodes and the cross straps are welded to the side rods. As mentioned, an advantage of this apparatus is that the entire lengths of the side rods 22 and 23 are maintained firmly against the mandrel sections during welding whereby the proper parallel spacing between the side rods is provided.

In another embodiment of the apparatus, welding electrodes 60 and 61 are provided as shown in FIGS. 8, 9

and 10. Each electrode 60 and 61 is provided with a longitudinally extending projection or ridge 63. The ridges 63 are wedge shaped, as shown, and the height of each ridge is slightly less than one half the thickness of the grid frame 40 including the cross straps 12. Each ridge is provided adjacent each end thereof with a transverse groove 65. As shown in FIG. 8 the walls 66 of grooves 65 taper towards each other, the distance between the walls at the bottom of the grooves being about equal to the width of the cross straps 12, and the opening between the walls 66 at the mouth of the grooves 65 being slightly greater than the width of the cross straps. Also, the grooves in each ridge are carefully spaced apart from each other a distance equal to the desired spacing between the cross strap pairs 12 of the grid frames 40.

Upon movement of the welding electrodes 60 and 61 together, as shown in FIGS. 9 and 10, ridges 63 are inserted between the adjacent side rods 22 and 23 and force them apart and against the mandrel sections 36 and 38 in a fashion similar to that described above. The grooves 65 register with the cross straps 12 and as the welding electrodes come together the tapered walls 66 of the grooves guide the cross straps into proper orientation with respect to the side rods. The floor of the grooves engage the cross straps and press them against the side rods, current then being pass-ed through the electrodes 60 and 61 for welding the cross straps 12 to the side rods 22 and 23.

In a still further embodiment of apparatus having utility when it is desired to make frames that do not have ears 13, the extending tongues (or ridges) are located near the side edge of the welding electrode face. When welding electrodes 68 and 69 incorporating this construction (FIG. 11) are brought together, tongue 70 extending from electrode 68 tends to force the two adjacent side rods 22 and 23 tightly against one another and against the mandrel 32. In this embodiment, the backup mandrel section is not employed.

Further embodiments and variations of the invention will be apparent to those skilled in the art.

What is claimed is:

1. In a method of producing frames for grid electrodes the steps of feeding pairs of closely adjacent side rods transversely to sets of spaced cross straps, wedging said side rods apart and outwardly against a mandrel while maintaining them parallel to one another, securing said cross straps to said side rods, and cutting said cross straps between said side rods.

2. In a method of producing frames for grid electrodes, the steps of providing spaced sets of cross straps, attaching a side rod to the leading ends of said cross straps, passing a mandrel transversely to said cross straps and into engagement with said side rod along one side of said mandrel, passing a pair of closely disposed side rods transversely to said cross straps and adjacent to said mandrel along the other side thereof, wedging apart said pair of side rods a predetermined distance and welding said cross straps to said wedged apart pair of side rods by moving portions of oppositely arranged welding electrodes into engagement with said cross straps and said pair of side rods and other portions of said welding electrodes between said pair of side rods, and cutting said cross straps between said pair of side rods.

3. In a method of producing frames for grid elec trodes, the steps of providing spaced sets of cross straps, attaching a first side rod to the leading ends of said cross straps, passing a pair of closely disposed side rods transversely to said cross strap and parallel to side first side rod, wedging apart said pair of side rods a predetermined distance and welding said cross straps to said wedged apart pair of side rods by moving portions of oppositely arranged welding electrodes into engagement with said cross straps and said pair of side rods and other portions of said welding electrodes between said pair of side rods, and cutting said cross strap between said pair of side rods.

References Cited by the Examiner UNITED STATES PATENTS 1,934,097 11/1933 Simon -112 X 2,182,968 12/1939 Lunsford.

2,256,428 9/1941 Green 29-417 2,332,022 10/1943 Southwick 219-56 2,455,346 11/1948 Wickwire 218-56 2,761,202 9/1956 Beare 29-417 3,054,165 9/1962 Braun et al 29-417 X CHARLIE T. MOON, Primary Examiner. WHITMORE A. WILTZ, Examiner. 

1. IN A METHOD OF PRODUCING FRAMES FOR GRID ELECTRODES THE STEPS OF FEEDING PAIRS OF CLOSELY ADJACENT SIDE RODS TRANSVERSELY TO SETS OF SPACED CROSS STRAPS, WEDGING SAID SIDE RODS APART AND OUTWARDLY AGAINST A MANDREL WHILE MAINTAINING THEM PARALLEL TO ONE ANOTHER, SECURING SAID CROSS STRAPS TO SAID SIDE RODS, AND CUTTING SAID CROSS STRAPS BETWEEN SAID SIDE RODS. 